The present invention relates to a vacuum pump to be used to discharge gas from a vacuum chamber installed on equipment for manufacturing semiconductors.
A vacuum pump for generating a vacuum environment is indispensable for a CVD apparatus, a dry etching apparatus, a sputtering apparatus, and an evaporating apparatus. In recent years, the demand for vacuum pumps having high operational performance has become stronger and stronger because the process of manufacturing semiconductors must be clean and have a high vacuum.
FIG. 9 shows an example of a screw type vacuum pump which is classified as a conventional positive displacement vacuum pump. The vacuum pump comprises a housing 21; a first rotary shaft 22; a second rotary shaft 23; cylindrical rotors 24 and 25 supported by the first rotary shaft 22 and the second rotary shaft 23, respectively; and thread grooves 26 and 27 formed on the peripheral surfaces of the rotors 24 and 25, respectively. That is, the conventional screw type vacuum pump comprises the first rotary shaft 22 and the second rotary shaft 23, parallel with each other and, accommodated in the housing 21; the rotors 24 and 25 mounted on the rotary shafts 22 and 23, respectively; and the thread grooves 26 and 27 formed on the rotors 24 and 25, respectively, to form screws. A space is formed between the thread grooves 26 and 27 by engagement between the groove of the thread groove 26 and the thread of the thread groove 27 and between the thread of the thread groove 26 and the groove of the thread groove 27. As a result of the rotation of the rotors 24 and 25, the volume of the space changes and thus suction and discharge (pumping) operations are performed. In this vacuum pump, the synchronous rotation of the rotors 24 and 25 is carried out by the operation of the timing gears 28 and 29. That is, the rotation of a motor 81 is transmitted from a driving gear 82 to an intermediate gear 83 and then to the timing gear 29 mounted on the shaft of the rotor 25. The phase between the rotational angles of the rotors 24 and 25 is adjusted by engagement between the timing gears 28 and 29. Lubricating oil 84 filled in a mechanical operating chamber accommodating the above gears transmitting the power of the motor 81 and rotating the rotors 24 and 25 synchronously is forcibly supplied to the gears. A mechanical seal 86 is provided between a fluid-operating chamber accommodating the rotors 24, 25 and the mechanical operating chamber 85 so as to prevent the lubricating oil 84 from penetrating into the fluid-operating chamber 85.
FIG. 10 shows a conventional thread groove type vacuum pump, having a turbine blade, which is classified into a kinetic vacuum pump. The vacuum pump comprises a housing 31; a cylindrical rotor 32; a turbine blade 33; and a thread groove 34. That is, the conventional thread groove type vacuum pump has the rotor 32 in the housing 31; the turbine blade 33 disposed at an upper portion of a side portion of the rotor 32; and the thread groove 34 disposed below the rotor 32. Each member imparts momentum to gas molecules, thus performing suction and discharge operations.
The conventional positive displacement vacuum pump discharges gas in the viscous flow region, the pressure of which is near atmospheric pressure, but the operational range thereof is as low as approximately 10.sup.-1 Pa. The operational range of the conventional thread groove type vacuum pump having the turbine blade is as high as approximately 10.sup.-8 Pa, but the thread groove type vacuum pump is incapable of discharging gas in the viscous flow region, the pressure of which is near atmospheric pressure. Therefore, a roughing operation is performed to a degree of 10.sup.0 to 10.sup.-1 Pa by a rotary pump (a positive displacement vacuum pump) and then, a predetermined high vacuum is generated by a turbo pump (a kinetic vacuum pump).
With the progress of composite semiconductor processing in recent years, multi-chamber systems for evacuating a plurality of vacuum chambers independently of each other has been mainly adopted. Evacuating equipment is required for each chamber in order to adopt the multi-chamber system. But the use of two kinds of vacuum pumps leads to a large evacuating apparatus.
One of the present inventors has already proposed a vacuum pump comprising a kinetic vacuum pump structure section and a positive displacement vacuum pump structure section comprising a plurality of shafts. The kinetic vacuum pump structure section is disposed on one of the shafts for driving rotors of the positive displacement vacuum pump structure section. A plurality of the shafts is controlled so that the shafts rotate synchronously. The vacuum pump generates a vacuum in a wide range from atmospheric pressure to a high vacuum.